In 1848, a Yorkshireman, Joseph Swan was the first credited inventor of the an electrically operated incandescent lamp. Swan's early lamps provided little luminous flux output, were short lived, and were operated from low voltage Direct current (DC) galvanic (i.e., electrochemical) cell source of electrical power, thus requiring a relatively high current for any appreciable power delivered to the lamp. This relatively high current required the power source to be co-located with the lamp or unacceptable transmission losses, due to the finite conductivity of copper, would be incurred. Even at that time copper was recognized, as the most economic electrical conduction material. Due to this "line loss" penalty (I.sup.2 R losses of the copper conductors) it was not practical to transmit low voltage power over significant distances. Hence, Swan's early incandescent lamp had limited application since co-location of the lamp and power source was mandatory. However, the Swan low voltage, high current, co-located power source concept for artificial illumination survives today in flashlights, many transport vehicle lighting systems (particularly automotive vehicles) and other applications.
In the 1870's Thomas Alva Edison became the foremost of the many rivals to Swan in the race to improve electric lighting via incandescent lamps. The problem was how could the electric light be effectively "divided", where the most effective source was the free-air carbon arc. The aforesaid limitation of low voltage incandescent lighting meant that it was necessary to have the power source almost co-located with each lamp in a building. The need was to have lighting in different rooms or areas driven from a remote power source but not suffer the relatively massive I.sup.2 R line losses associated with low voltage consumption devices. This became known as the "division of light" problem and it was soon recognized that electric power could be more efficiently distributed at higher voltage, than usually associated with galvanic cell sources. A given amount of power could be transmitted with considerably less conduction losses inherent in copper conductors if higher voltage could be employed. For example, if an early 20 watt, 5 Volt Swan type of lamp existed, it would require 4 Amperes of electrical current. If a 20 watt, 100 volt lamp existed it would require only 0.2 Amperes of current. Thus, if higher voltage lamps could be developed, the transmission losses could be reduced to the point where the electric power source could be remotely located at great distance from the consuming devices.
By 1879 Swan had developed an approximation to the requirement. Edison, while working on the improvement of the then DC generators (at that time they were called dynamos which were used for free-air carbon arc lighting ) contemplated their use in a centralized power generation and distribution system for lighting. Further, Edison recognized the need for a high voltage, low current lamp so a central power generating station could be used for incandescent lighting. In 1878 Edison began to develop incandescent lamps beyond the limitations of the Swan lamps of the time. Late in 1879 he discovered that a carbon filament remained stable in vacuo. This discovery led him to a viable "high resistance", i.e. 100 Ohms or so, filamentary type lamp. Thus, the concept of using a central generation of higher voltage DC power and distributing electric power by copper wire to remote locations to solve the "division-of-light" problem, became widely recognized as Edison's contribution. However, it is not widely understood that Edison can be described as one, if not the first system engineer for his concept of integrating the electrical generation, distribution, and utilization elements to get a consistent set of requirements for each element to optimize the total System!.
In September 1882 Edison, using steam engine driven electrical machines to generate DC electric power, opened the first commercial central power generating station on Pearl Street in New York City. It had 85 customers and 400 lamps on the two wire feeder-and-main system. Later it was converted to the famous Edison three wire system consisting of a positive potential line, and equal but negative potential line and a neutral line, usually at ground potential. The DC power was distributed and was continuous and non-varying. The alternating current (AC) power that dominates the world today was little more than an electrical curiosity at that time. In 1889 Edison's companies, including his electric light company, and the Sprague Electric Railway Company, merged to become the Edison General Electric Company and later merged with Thomson-Houston Electric Company to become the General Electric Company (GE) which we know today.
Another inventor, circa Edison's time, was Nikola Tesla, a Croatian emigre to the US. Early in his career he worked for Edison redesigning DC dynamos in New York City. After being turned down by Edison for a requested raise of his salary from $18.00 to $25.00 per month, Tesla offered to sell his inventions to Edison for $50,000. Edison jokingly rejected Tesla's offer, who then resigned and in 1887 formed his own company to exploit one of his conceived inventions. That invention was, and remains today, one of the truly great inventions of all time, i.e., the conceptual discovery of the rotating magnetic field and the adaptation of it to his polyphase induction motor. Further, it provided means for generating polyphase AC power which had the salient property of being continuous and non-varying, just like DC. This work led to a series of patents between 1888 and 1896 which were acquired by the entrepreneur George Westinghouse, founder of today's Westinghouse Electric Corporation. Today almost all of the world's power is generated, transmitted, and distributed by some form of the Tesla polyphase system and where applicable, the generated electrical power is turned back into mechanical energy by updated versions of the motors originally covered by his patents. Tesla was never widely recognized in the US for his outstanding inventive contributions due to his eccentricities. Some referred to him as the "Mad Croatian", Edison called him "the poet of Science" and thought him to be impractical.
However, Tesla's patents, which Edison declined to buy, were purchased by Westinghouse and became the cornerstone of Westinghouse's design and 1894 inauguration of the Niagara Falls Polyphase AC Hydroelectric plant, which soon changed the gas lighting era in cities to AC electric lighting and all but ended the celebrated war between Tesla's, i.e., Westinghouse's AC system and Edison's, DC system. A statue of Nikola Tesla stands on Goat Island, an island located in the Niagara river at the precipice of Niagara Falls, in recognition of his contribution. The continuing success of the Niagara Falls Hydroelectric plant which used the Tesla system was victorious and ended the so-called "AC vs DC war" in favor of AC. During that period Edison, whose lighting patents had been acquired by General Electric, stated that AC electric power was not commercially practical, and furthermore dangerous,.and he refused to adopt it. Nevertheless, with George Westinghouse's advocacy, the Tesla AC system made General Electric's DC system obsolete by the turn of the century. The economic value of the Tesla and Edison patents caused them to be the focus of animosity and litigation. Westinghouse and General Electric cooperated in an an electric manufacturing duopoly which continued at least until the passage and implementation of the Clayton Antitrust Act in 1911 and the later formation of RCA during World War I which combined to blunt the duopoly's control of electric and radio patents. One Tesla radio patent case continued until 1945 when the Supreme Court belatedly reversed over a quarter of a century of lower court rulings in favor of Tesla and against Marconi Wireless, by then a part of RCA.
The ability to generate polyphase AC power gave the world a practical source of continuous, non-varying electrical power, just as good as DC power. The availability of economical AC power led to the use of large polyphase induction motors to supply mechanical power to industry without the commutation (switching) problems of DC machinery. Furthermore AC power had the advantage of being able to have its voltage transformed to higher or lower voltages. Typically, AC power is simultaniously generated as three-time displaced single phases, i.e., poly phase. Each of the three phases alternates between positive and negative half cycles 60 times each second (50 Hertz in some parts of the world). It is then distributed as polyphase power until the aggregation of a consumer's electrical load is relatively small. When that occurs the supplier, i.e., the electric utility company, will branch off at an appropriate point within their electrical distribution system, one of the three phases to supply that consumer, i.e., residence, small group of residences, or smaller buildings. Larger commercial buildings will receive all three phases of the polyphase distributed power. Then the consumer in turn will deliver polyphase power to the larger building loads, i.e., large motors, such as the HVAC sub-system and to the buildings electrical distribution panels. From the electrical distribution panels, the power is usually distributed as single phase power to the smaller load devices. Since the building electrical lighting and appliance loads consist of widely distributed individual devices, they are generally designed to operate with single phase AC power. Hence, single phase branch circuits distribute the power to accommodate these single phase consumption devices. These single phase circuits generally have three wires, the "line" which is "hot", the neutral line which is "cold", and a saftey ground conductor. Care must be taken to insure that the electrical loads powered by the single phase branch circuits are more or less equally divided between the three different phases available so as not to vitiate the beneficial purpose of polyphase power, i.e., continuous, non varying power flow.
At the turn of this century incandescent lighting began to replace gas light and became the lighting of choice in commercial buildings until the 1940's when gas discharge lamps, based on Hg vapor excited, fluorescent material for visable light was perfected as an alternative (Westinghouse Electric first demonstrated what portended to be a commercially useful fluorescent gas discharge lamp (GDL), at the 1938 Chicago Worlds Fair). This new lamp had to have an auxiliary device to first cause lamp arc ignition and after ignition occurred, to limit the amplitude of the arc current since by itself the fluorescent lamp had no inherent current limiting mechanism when operated from a voltage source. Without an auxiliary device to stablize or limit the arc current, the lamp's arc would exceed its current rating and damage everything involved. In North and South America these auxiliaries have been combined into a single device called a ballast which provides means for lamp arc ignition, current limiting, and in some cases a necessary supply voltage transformation to accommodate different lamp lengths. The current limiting, i.e., ballast function, effectively establishes the arc current to a maximum fixed-arc level.
Despite the need for both a lamp and ballast, with the latter's attendant higher first cost, the fluorescent lamp soon began to replace the incandescent lamp in most commercial and industrial lighting applications. It had a much longer life, resulting in substantially reduced maintenance costs. Further, due to its physical linear nature it is was and remains a more distributive light.source, as opposed to the peak-valley or "spot" characteristic of the point source incandescent lamp it replaced. Still further, just as the incandescent lamp was a more efficient light source than the gas jet it replaced, the fluorescent lamp was two to three times more efficient than the incandescent lamp, in terms of luminous flux per unit of electric power consumed. However, much of the electric energy that could have been saved was lost due to an industry-driven high intensity lighting marketing trend which, in today's energy conservation environment, is considered beyond the need of human use.
By the 1960s the fluorescent lamp was ubiquitous in building lighting with more efficient phosphors and a variety of starting methods, i.e., pre-heat, rapid-start, or instant-start, had been developed. Advances in lamp electrode technology and phosphor coatings made the fluorescent lamp even more efficient and lamp life continued to increase. These fluorescent lamp improvements combined with inexpensive energy, brought about the unnecessary high illuminance lighting of over 100 foot candles (lumens per foot.sup.2) or over 1000 Lux (lumens per Meter.sup.2) that became common place in the 1960s and 70s.. Then came the infamous Oil Embargo of the 1970's, causing energy costs to spiral, and energy conservation came into vogue. It had been recognized that over half of the lighting energy consumed in commercial buildings was a costly waste of electric energy and the concomitant money.
However, the trend of wasteful overlighting had to continued until the lighting industry could design new replacement products like three lamp luminaires to replace four lamp luminaires and reduced wattage lamps, et al, to bring about less lighting electric power consumption while the industry attempted to increase market share dollar volumes. Typical of the pricing strategies is the tri-phosphor reduced wattage fluorescent lamp selling for three and four times the price of the industry standard, low cost, cool white, 40 watt F40 fluorescent lamp, which by the wisdom lobbied into the 1992 Energy Act of Congress, is scheduled to be outlawed in 1994. While the number of the new tri-phosphor T-8 lamps sold may decline, due to the requirement for less light, their increased cost indicates that the lamp industry's sales volume will increase. Similarly, luminaire manufact-urers have developed new reduced lamp population, high cutoff angle, parabolic polished aluminum reflector surface luminaires which sell at a cost of two and three times as much as the former commodity level, white painted, 4 lamp, prismatic lens diffuser luminaire.
The third new major lighting related device, spauned by the energy conservation movement, is the so-called "electronic ballast" which provides a nominal fixed-arc current to the lamp(s). These electronic ballasts, with up to a nominal 20% increase in efficacy, sell at prices 2 to 4 times the cost of the conventional ballast that they are meant to replace, and they generally require DC power which requires the conversion of AC to DC.
Not surprisingly, some of these new, more expensive, products met with some sales resistance until the electric power utility companies began to grant subsidies (i.e. money rebates) to purchasers of these new lighting products. The rationale behind the rebate was that these new products would reduce electric demand. The electric power utilities discovered that where the Public Service Commissions might resist electric energy rate increases for building new electric power generating facilities, the same commission would often grant the same requested rate increase if the utility company would spend the rate increase proceeds on electric energy conservation programs like giving an end user a "rebate" if a building was retrofited with the new reduced energy consuming lamps, luminaires and/or electronic ballasts. Some utilities discovered they could make more money by selling less through these giveaway programs. Thus, instead of the building owners paying for the new equipment the rate- paying public at large would pay for the retrofiting of these new products. This strategy was abetted, adopted and sold by some utility companies based on the hope that it would be able to delay the construction of new generating plants which use scarce resources and emit both thermal and material pollution.
Of anecdotal note, had modern day electronic technology been available during the DC AC war between Edison and Tesla (and their respective sponsors, General Electric and Westinghouse) during the 1880s-1890s, Westinghouse's AC approach might not have been the total victor. For example, in today's world and for a number of reasons, AC is converted to DC for long distance electric power transmission. A further example is today's increasing need for DC power is the widespread and increasing use of DC motors, from large elevator motors to small printer motors where again, AC has to be converted into DC. Still further, state of the art fluorescent lamp lighting, one of the largest consuming segments of electric energy, is now converting utility delivered AC power into DC before it is inverted back into higher frequency AC power. Had the Edisons and Teslas of their day only known what the future held, a split system, i.e., AC and DC, might have been developed to meet today's need for DC power. Converting AC to DC, while costly, is easily accomplished with todays technology. Converting polyphase AC into DC power (polyphase) is considerably less expensive single phase AC to DC. The conversion of single phase AC to DC is more expensive because in addition to the rectification of the AC into pulsating DC, energy storage elements are then required to convert the pulsating DC into an acceptable level of continuous, non-varying, DC power. These two methods of converting AC into DC as they apply to fluorescent GDL will be discussed in the summary and detail description sections below.
To date the lighting industry, including the electric power utility companies, in maintaining the use of fixed-arc current lamp operation have overlooked the energy saving strategy which dwarfs all other electric demand reducing strategies. The overlooked strategy, which offers more promise than the combined savings of the new, energy saving, lamps, fixed-arc electronic ballasts, and reduced population luminaries etc., is to operate the fluorescent lamp with an automatically adjusting variable-arc current. With fixed-arc current operation it is necessary to overlight at least by a factor of at least two to one for the following reasons.
First a building has to be overlit because the light output of a fluorescent lamp declines with its usage and/or lack of proper luminaire maintenance. The general rule applied to such lumen depreciation problems has been to overlight when lamps are new, with its concomitant waste of energy, in order to have enough light when lamps are aged, or, their light output degraded because of improper maintenance. Adopting this general rule of overlighting new lamps, leads to an average energy waste of at least 10 percent of the consumed electrical energy which can be saved if automatically adjusting variable-arc current lamp operation is adopted.
Secondly, as people age their visual acuity declines, e.g., the worker population in the fifties age group have less than half the visual acuity of the twenties age group. Thus buildings with fixed-arc lighting systems are designed to accommodate an older work population. The current standards established by the Illumination Engineering Society/American National Standards Institute (IES/ANSI) effectively state a lighting level of 200 Lux (nominally 20 foot candles) for general office work for a person under 40, and 300 Lux (nominally 30 foot candles) for a person between 40 to 55, and 500 Lux (nominally 50 foot candles) for the over 55 person. Since fixed-arc lighting precludes adjustment, buildings in general tend to light for the older age group. Therefore, age group related over-lighting causes at least a 30% energy waste which can be saved with variable-arc current lamp drive systems.
Third, fixed-arc current lghting also tends towards having uniform building lighting, hence public areas. i.e. corridors etc., which account for 10 to 15% of the building space, have several times more light than called for by the IES/ANSI standard of less than 10 foot candles in public spaces. This overlighting of public building spaces results in at least 5% of a building's overall lighting energy being wasted, which could be saved with variable-arc current lighting.
The fourth major lighting energy waste is that most building lighting systems in general are designed without regard for daylight other than its use as an additive light component to the fluorescent light. This overlighting strategy of not using daylight in lieu of fluorescent lighting, brought about by the rare need to use offices at night when no daylight is present, is totally wasteful in today's world. Variable-arc current lighting provides the "just right" amount of light at all times by automatically adjusting up or down as daylight increases or decreases, hence their is no longer any justification for overlighting. The total utilization of free daylight in modern "glass wall" buildings brings about an average overall building saving of electrical lighting energy of at least 30%.
Multiplying all the above described minimal energy saving factors, (5% due to the overlighting of corridors and public areas, 10% due to overlighting in order to have enough light when the lamps and luminaires are depreciated, 30% due to overlighting for worker population age group considerations and 30% due to failing to properly utilized free daylight), in lieu fluorescent lighting) together, i.e., (1 - 0.05) X (1 - 0.10) X (1 - 0.3) X (1 - 0.3) reduces the lighting to nominally 42% of the level required for fixed-arc lighting thus providing a potential reduction of 58% in the lighting energy consumed, and concomitant costs, if vari-able-arc lighting is utilized.
In addition, less lighing equates to less building heat load which the HVAC must dispose of, leading to even further savings, which are realized in particular during the summer months peak demand period(s). Further each office or building area can be lighted to meet the space, task, and/or an occupant's individual needs often leading to increased productivity, by being able to initially set the lamp's arc current to the proper night time lighting requirement and thereafter let the arc current automatically adjust and readjust whenever necessary, to maintain the just-right established lighting level. At anytime the building maintenance personnel can manually readjust the night time just right lighting level to accomodate the requirement if and when that space is reconfigured for other tasks or use. Hence, the building can have the just right level of light now and in the future, even when conditions vary.
Variable-arc current lighting has taken time to be develop and mature into reliable products because the fluorescent GDL is intrinsically a non-stable, highly non-linear both statically and dynamically, electronic device. Because of these characteristics, attempting to control the fluorescent GDL devices bring a host of "new" problems to electrical lighting never encountered with incandescent lighting. Many otherwise qualified companies and their engineers have attempted to develop variable-arc current control for fluorescent GDL devices but to date only a few have succeeded and fewer yet in a cost effective manner that meets the requirement of practical application.
When a fluorescent GDL is driven from a sinusoidal AC voltage source of power, the instantaneous power flow is by definition non-continuous, hence variable. If the single phase AC source were an ideal square wave current, power flow could conceivably be continuous and then ideal. Conversely, if during part of each AC half wave the voltage available is insufficient to sustain the lamp's arc, the GDL's plasma column will begin to de-ionize. These phenomena occur during each sinusoidal AC voltage half-cycle when the instantaneous voltage, impressed across the GDL, falls below a certain level. For example, a 40 Watt F40 T-12 fluorescent lamp requires a nominal instantaneous voltage of at least 100 volts between the lamp's two electrode pairs. Hence, if the nominal voltage applied to the lamp-ballast combination was 120 volts.sub.rms, the voltage sine wave would vary from zero to nominally 170 volt peak and the arc discharge could not be sustained in that portion of a given cycle where the applied voltage is less than the 100 volt required to sustain the arc discharge. During the period(s) of time of the applied voltage sine wave, when the instantaneous voltage is below the arc sustaining level, the plasma column is de-ionizing and re-ionizing. When lamps are operated with 50/60 Hertz AC power, the deionization and re-ionization phenomena of the GDL might take two (2) milliseconds out of each nominally 10 (for 50 Hertz or 8.33 . . . for 60 Hertz) milliseconds out of each AC half wave time period. It has long been known that if the driving frequency is raised to greater than the natural relaxation osccilation frequency of the plasma, increased lamp efficacy results. One of the reasons for the increase in efficacy is that, the anode fall voltage (on symmetrical AC of any waveshape, a lamp electrode operates alternately as a cathode, then an anode, then a cathode etc. for equal time intervals) drops a significant amount of voltage at the lower frequencies. Further, when the GDL is operated above the natural relaxation frequency of the plasma, the interval of current reversal now becomes sufficiently short that (less than 500 microseconds or so) that the loss of electrical energy into the arc for repeated deionization-reionization is significantly lower. These two factors account for the vast majority of the observed increase in lamp efficacy (luminous flux per watt of arc electric power).
The wide spread recognition that operating the arc plasma at a higher frequency brings higher lamp efficacy and other benefits, coupled with advances in the semiconductor industry and ever increasing electrical energy costs has spawned a movement to convert the AC driven magnetic ballasts to electronic ballasts. However, the latter require a DC link voltage which then has to be inverted into relatively high frequency AC, by appropiate electronic switching devices in order to improve fluorescent GDL efficacy as an energy conserving strategy. Therefore, pioneer developers of "electronic" ballasts have to employ AC to DC and DC to AC power conversion techniques with the latter at selected operating frequencies well above the natural relaxation oscillation of the arc's plasma, voice band telephony, and the human aural hearing frequencies. The selected frequency is usually of the order of 20 KiloHertz and above to avoid magnetostriction generated acoustic noise. This is higher than necessary for efficacy enhancement but working at these higher frequencies guarantees avoidance of the inherent aforementioned de-ionization re-ionization losses and the nominal 10 to 15 volt drop due to the electrical phenomena at the anode electrode whenever a fluorescent GDL lamp is operating at an AC frequency significantly below the natural relaxation oscillation frequency of the plasma. The 20 kHz exceeds the need to eliminate the cathode fall voltage, acoustic "noise" and/or the generation of voice band telephone system interference.
When a fluorescent GDL is operated significantly above the natural plasma frequency, a nominally greater than 10% reduction in power is achieved for a given luminous flux output compared to the same GDL whose arc current is operated with 50-60 Hertz power with a non square wave arc current wave form, i,e., a waveform approaching a sine wave. Care must be taken to suppress unacceptable levels of electromagnetic interference (EMI), one of the elements of the growing problem of "electro-pollution", that might otherwise be conductively coupled to the line frequency AC power source. There are two aspects of electro-pollution to be concerned with; 1, the generation of low frequency current harmonics of the line current being returned to the AC power distribution system; and, 2. the induction fields which surround the lamps plus some actual radiation at higher frequencies due to harmonics of the frequency driving the the arc plasma and the conduction of same back into the power line.
Generally the approach taken in the design of "electronic ballasts" is to base their design on utilizing the three wires (i.e., line which is "hot", neutral which is "cold", and the safety ground) single phase AC power source (60 Hertz in North and South America and 50 Hertz in most of Europe and Asia) of a single phase AC power branch circuit generally feeding each fluorescent lamp luminaire. However these same three AC wires could be utilized as conductors for a three wire "Edison" DC branch circuit, i.e., a positive potential DC line, a negative potential DC line and a neutral at the ground potential. To branch off single phases of the polyphase power and convert each of those single phases into DC co-located at the consuming site isn't as inefficient as directly converting the polyphase AC power into DC power. In the single phase AC case, the AC must be rectified and then an energy store must be provided to filter the rectified pulsating DC into a non-varying DC power source to supply the DC to AC converter section of the "electronic ballast". This approach to DC creates additional power factor and harmonic current problems which can and must be resolved by more expensive filtering. In the conversion of polyphase power to DC, the power factor and current harmonic problems associated with the single phase case, are not present and further, very little energy storage is required. In either rectification case, the continuous DC power, i.e., the DC link must always be supplied to the DC to AC inverter section of the "electronic ballast" which converts the continuous DC Link power back into AC but at a higher frequency. When the GDL(s) are driven from a high frequency power source, the required current limiting element, i.e., the ballast (either a capacitor, or inductor or combination thereof, connected in series with each lamp or lamps) become relatively small compared with the elements required in 50/60 Hertz AC powered systems.
Prior art also teaches that there are at least three common methods to gain lamp arc ignition. The first is called "instant start" wherein the voltage, at the time it is applied to the lamp, is sufficiently high to cause field effect electron emission from the cathode surface, and thus provide the initial electron current carriers to start the arc flowing. Thereafter the necessary electron emission from the lamp's cathode(s) is achieved by thermionic electron emission caused by the arc heating the cathode(s) via the anode fall and the cathode fall phenonema.
The second commonly used method for lamp arc ignition is called "Pre-heat or SwitchStart" wherein a current temporarily flows in the cathode heating element causing thermionic electron emission from the cathode for arc ignition. These emitted electrons act as the current carriers for the lamp arc. Once the lamp arc ignites, the externally applied cathode heater current is terminated and the ability of the cathode to emit electrons is sustained only by the arc created heating via cathode and anode falls at the electrodes.
The third and perhaps the most widely used lamp ignition method in the North and South America continents is called "Rapid Start" ignition wherein the lamp electrodes are heated by an external source both before and after arc ignition occurs. It is well known that GDL lamps operated "Rapid Start" have a longer lamp life than lamps operated "Pre-heat" and lamps operated "Pre-heat" tend to have longer useful lives than lamps operated "Instant-Start". Hence the slightly higher cost of a rapid start ballast is offset by longer lamp life and the resulting reduced lamp maintenance costs.
So far this discussion has been limited to ballasts which operate its associated lamps with a fixed-arc which is the nominally accepted standard for most of today's fluorescent lighting. While fixed-arc lighting is efficient relative to incandescent lighting, a great deal of energy is wasted. The principal shortcomings of fixed-arc current lighting will now be discussed.
One energy wasteful shortcoming of "fixed arc" lighting is that the useful life of the phosphor coating on the inside wall of the fluorescent tube, is slowly shortened by the energetic UV photons causing molecular disassociation of the phosphor molecules and the metal emissions from the cathodes causing a thin layer of metal overcoat the phosphors, i.e., sometimes noticed near the lamp ends and called end darkening wears over time; thus the light output steadily declines. Further, and well within the useful life of a lamp, both the lamp and the reflecting and transmission surfaces of the lamp luminaire accumulates light absorbing dust causing a further diminution of the useful portion of the generated light. Both users and light system designers recognize and sometimes refer to these problems as the "lumen maintenance design factor". In order that the lighted space never reach an underlighted condition, lighting system designers select the only solution to this problem of fixed-arc lighting systems which is to overlight the space when lamps are new and luminaires are clean so there is still sufficient light remaining when lamp light output at the luminaires reach depreciated states. On average, the amount of overlighting, sometimes called the "lumen maintenance design factor", can be as much as 30%. This need for designed-in over-lighting, results in an average electrical energy waste exceeding 10%.
This energy wasteful practice can be eliminated if the fixed arc could initially be adjusted to the "just-right" level and then have the arc plasma automatically adjust upward to maintain the initial luminous flux output of the luminaire and lamps lowers.
A second energy wasteful shortcoming of "fixed-arc" lighting relates to variations in visual acuity by different age groups. For example, the North America Illuminating Engineering Society (IES) has established guidelines which require upward lighting adjustments as much as 150% depending on the occupant age group and other factors. Since it is not practical to limit office occupants to younger age groups, buildings with "fixed-arc" office lighting levels must be designed accommodate the older age group worker population. In recognition of a person's visual acuity changing with age, the IES in their average weighting factor system (AWF) recommends higher light levels for older workers. For example purposes, IES lighting guidelines for category D (most often applied to general office work) calls for a lighting level of 200 Lux per square meter (nominally 20 foot candles, or lumens per square foot) if the task background reflectances are at least 70% and if the worker population is comprised of the under forty age group. If anyone in the working population is falls in the 40 to 55 age group that person(s) require 300 Lux, a 50% increase, and even more light for the yet older group age group and other factors. Thus buildings generally have to be overlit by at least 30% or more to include the liklyhood of older workers and thus avoid worker age discrimination. Variable-arc current lighting abolishes the need for age group compromised overlighting since the overlighting of the offices can be localized by it being lowered to the required "just right" level. Based on the assumption of an average office occupant age of 40 and offices comprise 80% of the building space, lighting energy savings of at least 20% can be realized with variable-arc current lighting.
The third and a major shortcoming of fixed-arc current lighting is that it does not utilize the free daylight contributions to sustain lighting in lieu of the costly electric lighting. The utilization of daylight contributions present in the majority of prime office space is left to the occupant getting up to turn the lights on when he needs the light and off when sufficient daylight is present and is noticed by an occupant. However in general the fluorescent luminaires are rarely turned off since overlighting is seldom noticed because when too much light is present a person's vision system simply adjusts by its iris constricting to limit the amount of light admitted to the vision system. Automatically adjusting variable-arc current lighting eliminates this waste by decreasing the arc current in relation to the amount of daylight entering each luminaire's area of illumination. Recorded tests with variable-arc current lighting indicate that the savings due to the daylight period of a day due to the roughly proportional reduction of the fluorescent lighting required, range from 30 to 64%. The majority of these savings occur when the sun is brightest and days are longer which usually corresponds with the peak summertime demand period when energy is often most costly and electric energy conservation most necessary and desirable. Daylight energy savings alone with variable-arc lighting will is estimated on average to reduce lighting energy consumption of the average building, at least 30%.
The fourth shortcoming of fixed-arc current lighting is its inability to vary background lighting levels hence, there is a tendency to select a general level of background lighting in office work areas capable of meeting all requirements. This approach leads to excess lighting in many areas. For example, the general office lighting level may be unsuitable for a CRT display of a personal computer or work station. Such improper lighting not only wastes energy but, can bring about glare problems with possible detrimental effects on work productivity. Variable-arc current lighting alleviates problems relating to task lighting in general by being able to adjust the background lighting level to the optimum level. Lacking building specifics, the ability to vary background lighting in terms of light energy savings is building and room geometry dependent. However, the ability to task light as required can be conservatively estimated to bring about at least a 10% energy savings.
Many other benefits flow from a changeover from fixed-arc lighting to variable-arc current lighting. Corridors with their longer duty cycles often account for up to 20% of the electrical lighting energy and often have the same 200, 300, and 500 Lux lighting level as offices despite the Illuminating Engineering Society (IES) and American National Standards Institute recommendations of 1/10 of the office lighting levels, i.e., 20, 30 and 50 Lux. Reduced electrical consumption also means less heat that the HVAC system must handle. All electrical lighting energy consumed for lighting purposes ultimately becomes heat which the building's HVAC system must handle. Of note, during the cold months when building heat is needed it is far more economical to generate the required heating BTU's from the building's heating system than by generating unnecessary lighting by-product BTUs. The above comments relate to the conservation of electrical energy through the adoption of variable-arc current lighting to eliminate totally unnecessary energy waste which is required in any building which utilize fixed-arc lighting. Still other benefits flow from eliminating the inherently wasteful practices discussed above, i.e., the economic benefits flowing to the building owner in that by substantially reducing electrical demand for lighting, e.g., a major New York building operating costs can be reduced by hundreds of thousands of dollars. Further, it helps the environment in the sense that each kWh of electrical energy saved means one less kWh has to be generated thus lessening the inherent thermal and particle pollution of land, air and water that electrical power generating plants brings about.